Brønsted Acids Promote Olefin Oxidations by Bioinspired Nonheme CoIII(PhIO)(OH) Complexes: A Role for Low-Barrier Hydrogen Bonds

Dongru Sun, Zhimin Wu, Xuan Zhang, Jindou Yang, Yufen Zhao, Wonwoo Nam, Yong Wang

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Introduction of Brønsted acids into biomimetic nonheme reactions promotes the oxidative ability of metal-oxygen complexes significantly. However, the molecular machinery of the promoted effects is missing. Herein, a comprehensive investigation of styrene oxidation by a cobalt(III)-iodosylbenzene complex, [(TQA)CoIII(OIPh)(OH)]2+ (1, TQA = tris(2-quinolylmethyl)amine), in the presence and absence of triflic acid (HOTf) was performed using density functional theory calculations. Results revealed for the first time that there is a low-barrier hydrogen bond (LBHB) between HOTf and the hydroxyl ligand of 1, which forms two valence-resonance structures [(TQA)CoIII(OIPh)(HO--HOTf)]2+ (1LBHB) and [(TQA)CoIII(OIPh)(H2O-OTf-)]2+ (1′LBHB). Due to the oxo-wall, these complexes (1LBHB and 1′LBHB) cannot convert to high-valent cobalt-oxyl species. Instead, styrene oxidation by these oxidants (1LBHB and 1′LBHB) shows novel spin-state selectivity, i.e., on the ground closed-shell singlet state, styrene is oxidized to an epoxide, whereas on the excited triplet and quintet states, an aldehyde product, phenylacetaldehyde, is formed. The preferred pathway is styrene oxidation by 1′LBHB, which is initiated by a rate-limiting bond-formation-coupled electron transfer process with an energy barrier of 12.2 kcal mol-1. The nascent PhIO-styrene-radical-cation intermediate undergoes an intramolecular rearrangement to produce an aldehyde. The halogen bond between the OH-/H2O ligand and the iodine of PhIO modulates the activity of the cobalt-iodosylarene complexes 1LBHB and 1′LBHB. These new mechanistic findings enrich our knowledge of nonheme chemistry and hypervalent iodine chemistry and will play a positive role in the rational design of new catalysts.

Original languageEnglish
Pages (from-to)5739-5749
Number of pages11
JournalJournal of the American Chemical Society
Volume145
Issue number10
DOIs
StatePublished - 15 Mar 2023

Bibliographical note

Funding Information:
This work is supported by the National Natural Science Foundation of China (No. 21873052), the National Research Foundation (NRF) of Korea (No. NRF-2021R1A3B1076539 to W.N.), the Natural Science Foundation of Zhejiang Province (No. LQ20B030004), the Ningbo Natural Science Foundation (No. 202003N4079), the Scientific Research Grant of Ningbo University (No. 215-432000282), and the Ningbo Top Talent Project (No. 215-432094250). Y.W. acknowledges Professor Hui Chen at the Institute of Chemistry, CAS, for the fruitful discussion.

Publisher Copyright:
© 2023 American Chemical Society

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